Hello Marta,
Thank you for posting in Microsoft Community.
I understand the need to insert a SIM card in your Surface Pro 8.
Yes, the Surface Pro 8 has a SIM card slot that supports both LTE and 5G connectivity. You can insert a nano-SIM card into the slot located on the left side of the device. You can refer to the steps below:
Place your Surface Pro 8 screen on a table and lift the kickstand to reveal the SIM door.
Insert the included SIM ejector tool into the small hole on the SIM door to detach it.
Push your SIM card into the SIM card slot until it clicks.
Slide the SIM door into place, then press down until it clicks.
Check this link to see more information: Insert a SIM card into your Surface - Microsoft Support
Hopefully this helps!
Best regards,
Rolando S.